A more thorough explanation:

Ad vitam means "for life."

• The prisoner was sentenced to ad vitam imprisonment.
• The soldier was awarded a medal ad vitam.

These examples show that ad vitam is used to describe something that is meant to last for the rest of one's life. In the first example, the prisoner will be in prison for the rest of their life. In the second example, the soldier was given a medal that they can keep for the rest of their life.